Well, I came up with the idea of running 8miles everyday for a year to raise awareness for a charity and maybe some money and the charity liked the idea and wanted to get some more people involved but we didnt get anyone because supposedly it was too much (people have jobs, family, kids etc) so decides to lower the mileage so to attract more runners.
4sounds like a doable distance for a lot of people so settled on 4. Most of the people I'm talking to are doing in the kilometres so it's 6.4k

I'm doing 4 for this, along with my marathon training,sprint training and swimming so should be fun